Internal combustion engines, including diesel engines, gasoline engines, gaseous fuel-powered engines, and other engines known in the art exhaust a complex mixture of air pollutants. These air pollutants are composed of gaseous compounds, such as, for example, the oxides of nitrogen (NOx). Due to increased awareness of the environment, exhaust-emission standards have become more stringent, and the amount of NOx emitted from an engine may be regulated depending on the type of engine, size of engine, and/or class of engine. In order to ensure compliance with the regulation of these compounds, some engine manufacturers have implemented a strategy called Selective Catalytic Reduction (SCR). SCR is a process where a gaseous or liquid reductant or reducing agent, e.g., a urea/water solution, is added to the exhaust gas stream of an engine and absorbed onto a catalyst. The reducing agent reacts with NOx in the exhaust gas to form H2O and N2, thereby reducing harmful emissions. The reducing agent is typically stored in a tank that has a supply line for providing the reducing agent to the exhaust stream.
Engines are often used in machines or in stationary applications that are located in extreme cold temperature environments. The cold temperature environments are particularly harsh on an engine when the engine is shut off over extended periods of time, such as overnight. In cold temperature environments, for example, when the ambient air temperature is less than −11° C., the reducing agent may freeze, either in the tank and/or in the supply line. In view of increased demands of exhaust emission standards, the reducing agent needs to be liquefied such that the exhaust stream receives the required dosage of reducing agent from the tank. Furthermore, the reducing agent needs to be liquefied within a certain time period after engine starting to ensure that the engine meets the exhaust emission standards within a certain amount of time after engine starting.
One system for heating a reducing agent is described in U.S. Patent Application Publication No. 2007/0079599 (the '599 application), published on Apr. 12, 2007 in the name of Osaku et al. and assigned to Nissan Diesel Motor Co., Ltd. The '599 application discloses a system that uses cooling water from an engine as a heat carrier to heat urea water in a urea storage tank via a heat exchanger pipe routed through the urea storage tank.
Although the system disclosed in the '599 application may provide a system for heating a reducing agent, the system does not address all of the requirements listed above. For example, the engine must warm up and heat the cooling water circulating therein prior to having any heat exchanging effect on the reducing agent. Since this may create a delay from when the engine is started to when the cooling water can deliver a heating effect to the reducing agent, the engine may fail to satisfy exhaust emission standards within the required time period. This is due to the reducing agent not being sufficiently thawed, and thus the nitrogen oxide reduction is not sufficiently completed prior to expelling the exhaust gases from the engine.
The disclosed system is directed to addressing the desire to have a liquefied reducing agent available shortly after the start-up of the engine.